Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, stars, nebulae and comets. More all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, the study of the Universe as a whole. Astronomy is one of the oldest of the natural sciences; the early civilizations in recorded history, such as the Babylonians, Indians, Nubians, Chinese and many ancient indigenous peoples of the Americas, performed methodical observations of the night sky. Astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, but professional astronomy is now considered to be synonymous with astrophysics. Professional astronomy is split into theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, analyzed using basic principles of physics.
Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs still play an active role in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets. Astronomy means "law of the stars". Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin, they are now distinct. Both of the terms "astronomy" and "astrophysics" may be used to refer to the same subject. Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties," while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, dynamic processes of celestial objects and phenomena."
In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject. However, since most modern astronomical research deals with subjects related to physics, modern astronomy could be called astrophysics; some fields, such as astrometry, are purely astronomy rather than astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics" depending on whether the department is affiliated with a physics department, many professional astronomers have physics rather than astronomy degrees; some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, Astronomy and Astrophysics. In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye.
In some locations, early cultures assembled massive artifacts that had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye; as civilizations developed, most notably in Mesopotamia, Persia, China and Central America, astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, the nature of the Sun and the Earth in the Universe were explored philosophically; the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Ptolemaic system, named after Ptolemy.
A important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the astronomical traditions that developed in many other civilizations. The Babylonians discovered. Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model. In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and inven
Adoption of the Gregorian calendar
The adoption of the Gregorian Calendar was an event in the modern history of most nations and societies, marking a change from their traditional dating system to the modern dating system, used around the world today. Some countries adopted the new calendar from 1582, some did not do so before the early twentieth century, others did so at various dates between. For many the new style calendar is only used for civil purposes and the old style calendar remains used in religious contexts. Today, the Gregorian calendar is the world's most used civil calendar. During – and for some time after – the change between systems, it has been common to use the terms Old Style and New Style when giving dates, to indicate which calendar was used to reckon them; the Gregorian calendar was decreed in 1582 by the papal bull Inter gravissimas by Pope Gregory XIII, to correct a divergence in the canonical date of the spring equinox from observed reality that affected the calculation of the date of Easter. Although Gregory's reform was enacted in the most solemn of forms available to the Church, the bull had no authority beyond the Catholic Church and the Papal States.
The changes he was proposing were changes to the civil calendar, over which he had no formal authority. They required adoption by the civil authorities in each country to have legal effect; the bull became the canon law of the Catholic Church in 1582, but it was not recognised by Protestant churches, Eastern Orthodox Churches, a few others. The days on which Easter and related holidays were celebrated by different Christian churches again diverged. A month after having decreed the reform, the pope granted to one Antoni Lilio the exclusive right to publish the calendar for a period of ten years; the Lunario Novo secondo la nuova riforma was printed by Vincenzo Accolti, one of the first calendars printed in Rome after the reform, notes at the bottom that it was signed with papal authorization and by Lilio. The papal brief was revoked on 20 September 1582, because Antonio Lilio proved unable to keep up with the demand for copies. Catholic states such as France, the Italian principalities, Spain and the Catholic states of the Holy Roman Empire were first to change to the Gregorian calendar.
Thursday, 4 October 1582 was followed by 15 October 1582, with ten days skipped. Countries that did not change until the 18th century had by observed an additional leap year, necessitating the dropping of eleven days; some countries did not change until the 19th or 20th century, necessitating one or two further days to be omitted from the calendar. Philip II of Spain decreed the change from the Julian to the Gregorian calendar, which affected much of Roman Catholic Europe, as Philip was at the time ruler over Spain and Portugal as well as much of Italy. In these territories, as well as in the Polish–Lithuanian Commonwealth and in the Papal States, the new calendar was implemented on the date specified by the bull, with Julian Thursday, 4 October 1582, being followed by Gregorian Friday, 15 October 1582. Other Catholic countries soon followed. France adopted the new calendar with Sunday, 9 December 1582, being followed by Monday, 20 December 1582; the Dutch provinces of Brabant and Zeeland, the States General adopted it on 25 December of that year.
The seven Catholic Swiss cantons adopted the new calendar in January 1684 while Geneva and several Protestant cantons adopted it in January 1701 or at other dates throughout the 18th century. The two Swiss communes of Schiers and Grüsch were the last areas of Western and Central Europe to switch to the Gregorian calendar, in 1812. Many Protestant countries objected to adopting a Catholic innovation. In England, Queen Elizabeth I and her privy council had looked favourably to a Gregorian-like royal commission recommendation to drop 10 days from the calendar but the virulent opposition of the Anglican bishops, who argued that the Pope was undoubtedly the fourth great beast of Daniel, led the Queen to let the matter be dropped. In the Czech lands, Protestants resisted the calendar imposed by the Habsburg Monarchy. In parts of Ireland, Catholic rebels until their defeat in the Nine Years' War kept the "new" Easter in defiance of the English-loyal authorities; the Lutheran Duchy of Prussia, until 1657 still a fiefdom of Roman Catholic Poland, was the first Protestant nation to adopt the Gregorian calendar.
Under influence of its liege lord, the King of Poland, it agreed in 1611 to do so. So 22 August was followed by 2 September 1612. However, this calendar change did not apply for other territories of the Hohenzollern, such as Berlin-based Brandenburg, a fief of the Holy Roman Empire. Through Ole Rømer's influence, Denmark in 1700, which included Norway, adopted the solar portion of the Gregorian calendar with Sunday, 18 February 1700, being followed by Monday, 1 March 1700 with the Brandenburg-Pomerania and other Protestant estates of the Holy Roman Empire. None of these st
Groundwater is the water present beneath Earth's surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water; the depth at which soil pore spaces or fractures and voids in rock become saturated with water is called the water table. Groundwater is recharged from and flows to the surface naturally. Groundwater is often withdrawn for agricultural and industrial use by constructing and operating extraction wells; the study of the distribution and movement of groundwater is hydrogeology called groundwater hydrology. Groundwater is thought of as water flowing through shallow aquifers, but, in the technical sense, it can contain soil moisture, immobile water in low permeability bedrock, deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can influence the movement of faults, it is that much of Earth's subsurface contains some water, which may be mixed with other fluids in some instances.
Groundwater may not be confined only to Earth. The formation of some of the landforms observed on Mars may have been influenced by groundwater. There is evidence that liquid water may exist in the subsurface of Jupiter's moon Europa. Groundwater is cheaper, more convenient and less vulnerable to pollution than surface water. Therefore, it is used for public water supplies. For example, groundwater provides the largest source of usable water storage in the United States, California annually withdraws the largest amount of groundwater of all the states. Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes in the US, including the Great Lakes. Many municipal water supplies are derived from groundwater. Polluted groundwater is less visible and more difficult to clean up than pollution in rivers and lakes. Groundwater pollution most results from improper disposal of wastes on land. Major sources include industrial and household chemicals and garbage landfills, excessive fertilizers and pesticides used in agriculture, industrial waste lagoons and process wastewater from mines, industrial fracking, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems.
An aquifer is a layer of porous substrate that transmits groundwater. When water can flow directly between the surface and the saturated zone of an aquifer, the aquifer is unconfined; the deeper parts of unconfined aquifers are more saturated since gravity causes water to flow downward. The upper level of this saturated layer of an unconfined aquifer is called the water table or phreatic surface. Below the water table, where in general all pore spaces are saturated with water, is the phreatic zone. Substrate with low porosity that permits limited transmission of groundwater is known as an aquitard. An aquiclude is a substrate with porosity, so low it is impermeable to groundwater. A confined aquifer is an aquifer, overlain by a impermeable layer of rock or substrate such as an aquiclude or aquitard. If a confined aquifer follows a downward grade from its recharge zone, groundwater can become pressurized as it flows; this can create artesian wells that flow without the need of a pump and rise to a higher elevation than the static water table at the above, aquifer.
The characteristics of aquifers vary with the geology and structure of the substrate and topography in which they occur. In general, the more productive aquifers occur in sedimentary geologic formations. By comparison and fractured crystalline rocks yield smaller quantities of groundwater in many environments. Unconsolidated to poorly cemented alluvial materials that have accumulated as valley-filling sediments in major river valleys and geologically subsiding structural basins are included among the most productive sources of groundwater; the high specific heat capacity of water and the insulating effect of soil and rock can mitigate the effects of climate and maintain groundwater at a steady temperature. In some places where groundwater temperatures are maintained by this effect at about 10 °C, groundwater can be used for controlling the temperature inside structures at the surface. For example, during hot weather cool groundwater can be pumped through radiators in a home and returned to the ground in another well.
During cold seasons, because it is warm, the water can be used in the same way as a source of heat for heat pumps, much more efficient than using air. The volume of groundwater in an aquifer can be estimated by measuring water levels in local wells and by examining geologic records from well-drilling to determine the extent and thickness of water-bearing sediments and rocks. Before an investment is made in production wells, test wells may be drilled to measure the depths at which water is encountered and collect samples of soils and water for laboratory analyses. Pumping tests can be performed in test wells to determine flow characteristics of the aquifer. Groundwater makes up about twenty percent of the world's fresh water supply, about 0.61% of the entire world's water, including oceans and permanent ice. Global groundwater storage is equal to the total amount of freshwater stored in the snow and ice pack, including the north and south poles; this makes it an important resource that can act as a natural storage that can buffer against shortages of surface water, as in during times of drought.
Groundwater is replenished b
A calendar is a system of organizing days for social, commercial or administrative purposes. This is done by giving names to periods of time days, weeks and years. A date is the designation of a specific day within such a system. A calendar is a physical record of such a system. A calendar can mean a list of planned events, such as a court calendar or a or chronological list of documents, such as a calendar of wills. Periods in a calendar are though not synchronised with the cycle of the sun or the moon; the most common type of pre-modern calendar was the lunisolar calendar, a lunar calendar that adds one intercalary month to remain synchronised with the solar year over the long term. The term calendar is taken from calendae, the term for the first day of the month in the Roman calendar, related to the verb calare "to call out", referring to the "calling" of the new moon when it was first seen. Latin calendarium meant "account book, register"; the Latin term was adopted in Old French as calendier and from there in Middle English as calender by the 13th century.
A calendar can be on paper or electronic device. The course of the sun and the moon are the most salient natural recurring events useful for timekeeping, thus in pre-modern societies worldwide lunation and the year were most used as time units; the Roman calendar contained remnants of a ancient pre-Etruscan 10-month solar year. The first recorded physical calendars, dependent on the development of writing in the Ancient Near East, are the Bronze Age Egyptian and Sumerian calendars. A large number of Ancient Near East calendar systems based on the Babylonian calendar date from the Iron Age, among them the calendar system of the Persian Empire, which in turn gave rise to the Zoroastrian calendar and the Hebrew calendar. A great number of Hellenic calendars developed in Classical Greece, in the Hellenistic period gave rise to both the ancient Roman calendar and to various Hindu calendars. Calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years.
This was based on observation, but there may have been early attempts to model the pattern of intercalation algorithmically, as evidenced in the fragmentary 2nd-century Coligny calendar. The Roman calendar was reformed by Julius Caesar in 45 BC; the Julian calendar was no longer dependent on the observation of the new moon but followed an algorithm of introducing a leap day every four years. This created a dissociation of the calendar month from the lunation; the Islamic calendar is based on the prohibition of intercalation by Muhammad, in Islamic tradition dated to a sermon held on 9 Dhu al-Hijjah AH 10. This resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year; the first calendar reform of the early modern era was the Gregorian calendar, introduced in 1582 based on the observation of a long-term shift between the Julian calendar and the solar year. There have been a number of modern proposals for reform of the calendar, such as the World Calendar, International Fixed Calendar, Holocene calendar, the Hanke-Henry Permanent Calendar.
Such ideas are mooted from time to time but have failed to gain traction because of the loss of continuity, massive upheaval in implementation, religious objections. A full calendar system has a different calendar date for every day, thus the week cycle is by itself not a full calendar system. The simplest calendar system just counts time periods from a reference date; this applies for Unix Time. The only possible variation is using a different reference date, in particular, one less distant in the past to make the numbers smaller. Computations in these systems are just a matter of subtraction. Other calendars have one larger units of time. Calendars that contain one level of cycles: week and weekday – this system is not common year and ordinal date within the year, e.g. the ISO 8601 ordinal date systemCalendars with two levels of cycles: year and day – most systems, including the Gregorian calendar, the Islamic calendar, the Solar Hijri calendar and the Hebrew calendar year and weekday – e.g. the ISO week dateCycles can be synchronized with periodic phenomena: Lunar calendars are synchronized to the motion of the Moon.
Solar calendars are based on perceived seasonal changes synchronized to the apparent motion of the Sun. Lunisolar calendars are based on a combination of both solar and lunar reckonings; the week cycle is an example of one, not synchronized to any external phenomenon. A calendar includes more than one type of cycle, or has both cyclic and non-cyclic elements. Most calendars incorporate more complex cycles. For example, the vast majority of them track years, months and days; the seven-day week is universal, though its use varies. It has run uninterrupted for millennia. Solar calendars assign a date to each solar day. A day may consist of the period between sunrise and sunset, with
Anno Mundi, abbreviated as AM, or Year After Creation, is a calendar era based on the biblical accounts of the creation of the world and subsequent history. Two such calendar eras have seen notable use historically: The Byzantine calendar was used in the Byzantine Empire and many Christian Orthodox countries and Eastern Orthodox Churches and was based on the Septuagint text of the Bible; that calendar is similar to the Julian calendar except that its epoch is equivalent to 1 September 5509 BC on the Julian proleptic calendar. Since the Middle Ages, the Hebrew calendar has been based on rabbinic calculations of the year of creation from the Hebrew Masoretic text of the bible; this calendar is used within Jewish communities for other purposes. On the Hebrew calendar, the day begins at sunset; the calendar's epoch, corresponding to the calculated date of the world's creation, is equivalent to sunset on the Julian proleptic calendar date 6 October 3761 BC. The new year begins at Rosh Hashanah in September.
Year anno mundi 5779, or AM 5779, began at sunset on 9 September 2018 on the Gregorian calendar. While differences in biblical interpretation or in calculation methodology can produce some differences in the creation date, most results fall close to one of these two dominant models; the primary reason for the disparity seems to lie in. Most of the 1,732-year difference resides in numerical discrepancies in the genealogies of the two versions of the Book of Genesis. Patriarchs from Adam to Terah, the father of Abraham, are said to be older by as much as 100 years or more when they begat their named son in the Greek Septuagint than they were in the Latin Vulgate or the Hebrew Tanakh; the net difference between the two major genealogies of Genesis is 1466 years, 85% of the total difference. During the Talmudic era, from the 1st to the 10th centuries AD, the center of the Jewish world was in the Middle East in the Talmudic Academies in Babylonia and Syria Palaestina. Jews in these regions used Seleucid Era dating as the primary method for calculating the calendar year.
For example, the writings of Josephus and the Books of the Maccabees used Seleucid Era dating and the Talmud tractate Avodah Zarah states: Rav Aha b. Jacob put this question: How do we know that our Era is connected with the Kingdom of Greece at all? Why not say that it is reckoned from the Exodus from Egypt, omitting the first thousand years and giving the years of the next thousand? In that case, the document is post-dated! Said Rav Nahman: In the Diaspora the Greek Era alone is used, he thought that Rav Nahman wanted to dispose of him anyhow, but when he went and studied it he found that it is indeed taught: In the Diaspora the Greek Era alone is used. In Talmudic writings, reference was made to other starting points for eras, such as Destruction Era dating, being the number of years since the AD 70 destruction of the Second Temple, the number of years since the Creation year based on the calculation in the Seder Olam Rabbah of Rabbi Jose ben Halafta in about AD 160. By his calculation, based on the Masoretic Text and Eve were created on 1st of Tishrei in 3760 BC confirmed by the Muslim chronologist al-Biruni as 3448 years before the Seleucid era.
An example is the c. 8th-century AD Baraita of Samuel. In the 8th and 9th centuries AD, the center of Jewish life moved from Babylonia to Europe, so calculations from the Seleucid era "became meaningless". From the 11th century, anno mundi dating became dominant throughout most of the world's Jewish communities, replacing the Seleucid dating system; the new system reached its definitive form in AD 1178. In the section Sanctification of the Moon, he wrote of his choice of Epoch, from which calculations of all dates should be made, as "the third day of Nisan in this present year..., the year 4938 of the creation of the world". He included all the rules for the calculated calendar epoch and their scriptural basis, including the modern epochal year in his work, establishing the final formal usage of the anno mundi era; the first year of the Jewish calendar, Anno Mundi 1, began about one year before Creation, so that year is called the Year of emptiness. The first five days of Jewish Creation week occupy the last five days of AM 1, Elul 25–29.
The sixth day of Creation, when Adam and Eve were created, is the first day of Rosh Hashanah. Its associated molad Adam occurred on Day 5 at 14 hours. A year earlier, the first day of AM 1, Rosh Hashanah, is associated with molad tohu, so named because it occurred before Creation when everything was still chaotic—it is translated as the new moon of nothing; this is called molad BaHaRaD, because it occurred on Day 2, 5 hours, 204 parts. Because this is just before midnight when the Western day begins, but after 6 pm when the Jewish calendrical day begins, its Julian calendar date is 6/7 October 3761 BC; the Septuagint was the most scholarly non-Hebrew version of the Old Testament available to early Christians